The polygraph in doubt

Because of the nature of deception, there is no good way to validate the test for making judgments about criminal behavior.

July/August 2004, Vol 35, No. 7

Print version: page 71

Psychologists have repeatedly told U.S. courts that polygraph tests--popularly thought to reveal a person's truthfulness through assessment of physiological states--are theoretically unsound and not valid in assessing honesty.

Explains psychologist Leonard Saxe, PhD, a professor and polygraph researcher at Brandeis University, "Because of the nature of deception, there is no good way to validate the test for making judgments about criminal behavior. There is no unique physiological reaction to deception."

Recent formal documentation of this comes from a National Research Council (NRC) blue ribbon panel appointed a year ago to examine the scientific validity of the polygraph for national security. Many psychologists served on the panel, including Paul Ekman, PhD, a longtime researcher of deception detection (see main article). The panel's report to NRC found no evidence of polygraph validity.

And theirs isn't the first scientific report to case doubt on the measure. In fact, due to such skepticism, the U.S. Supreme Court decided in a 1998 case involving military courts that a defendant did not have a right to introduce polygraph evidence. The Supreme Court decision cited scientific judgments about the accuracy of the test.

This decision, along with a 1988 law banning the use of polygraph tests of most employees, has led to a marked reduction in reliance on polygraph testing, notes Saxe. The ruling helped to dampen the tests' use in state and federal court, where the results are rarely accepted as evidence.

--R. ADELSON

Further Reading

The National Research Council report on the polygraph is available at www.nas.edu/nrc.